Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.49   6.702%   $124.2972   $124.30   $124.30   $124.30  
  Purchase #2 $218.59   3.466%   $226.1663   $226.17   $226.15   $226.20  
  Purchase #3 $174.89   7.384%   $187.8039   $187.80   $187.80   $187.80  
  Purchase #4 $232.62   9.622%   $255.0027   $255.00   $255.00   $255.00  
  Purchase #5 $93.52   5.530%   $98.6917   $98.69   $98.70   $98.70  
  Purchase #6 $155.29   3.460%   $160.663   $160.66   $160.65   $160.70  
  Purchase #7 $218.61   11.365%   $243.455   $243.46   $243.45   $243.50  
  7 purchase totals = $1,210.01       $1,296.0798   $1,296.08   $1,296.05   $1,296.20